1. Field of the Invention
This invention relates to a novel random 1-butene/ethylene copolymer having excellent utility. More specifically, it relates to a random 1-butene/ethylene copolymer having excellent transparency, surface nontackiness, tensile properties and other properties, which is suitable for the production of packaging films or sheets or other melt-molded articles having excellent transparency, antiblocking property, etc.
2. Description of the Prior Art
Heretofore, vinyl chloride resins have predominantly been used in the field of molding flexible or semirigid resins, but because of the evolution of corrosive gases during their incineration after discharging and the suspected safety of residual monomers or plasticizers therein, it has been desired to replace them by olefinic flexible or semirigid resins.
Olefinic copolymers such as ethylene copolymers, propylene copolymers, and 1-butene copolymers have recently been utilized in the field of molding such flexible or semirigid resins. Many proposals have been made on flexible 1-butene random copolymers composed of 1-butene as a main component and propylene. U.S. Pat. Nos. 3,278,504, 3,332,921 and 4,168,361, British Patents Nos. 1,018,341 and 1,084,953 and Japanese Laid-Open Patent Publication No. 38787/1975 (corresponding to U.S. Pat. No. 3,923,758) disclose 1-butene random copolymers produced by using titanium trichloride or titanium tetrachloride catalysts.
The above-cited U.S. Pat. No. 3,278,504 describes that a propylene/1-butene copolymer having a 1-butene content of 30 to 70 mole % is produced by using titanium tetrachloride or titanium trichloride. The present inventors have found, however, that the copolymer produced with such a catalyst system is a flexible resin which has a boiling methyl acetate-soluble content of more than 2% by weight and a high acetone/n-decane mixture (1:1 by volume)-soluble content, surface tackiness, and inferior transparency.
The above-cited U.S. Pat. No. 3,332,921 and British Patent No. 1,084,953 propose various 1-butene copolymers having varying 1-butene contents which are produced by using a titanium trichloride catalyst. The present inventors, however, have found that among these 1-butene copolymers, those having a 1-butene content of 60 to 99 mole % have the same disadvantages as the 1-butene copolymer described in the above-cited U.S. Pat. No. 3,278,504.
In the above-cited British Patent No. 1,018,341, copolymers having a 1-butene content of 25 to 90 mole % are prepared by using a catalyst comprising a transition metal halide such as titanium trichloride and a derivative of phosphoric acid. The present inventors, however, have found that among the copolymers specifically disclosed in this British Patent, those having a 1-butene content of 50 to 90 mole % have an acetone-soluble content of at least 1.5% by weight. Investigations of the present inventors have shown that these copolymers have a boiling methyl acetate-soluble content of more than 2% by weight and an acetone/n-decane mixed solvent (1:1 by volume)-soluble content of more than 5 .times. [.eta.].sup.-1.2 and that these 1-butene copolymers give molded articles having high surface tackiness and inferior transparency.
The above-cited U.S. Pat. No. 4,168,361 discloses propylene/1-butene copolymers having a propylene content of 40 to 90 mole %. Investigations of the present inventors, however, have shown that among these copolymers, those having a 1-butene content of 50 to 60 mole % have a high acetone/n-decane mixed solvent-soluble content, and only give molded articles having high surface tackiness and inferior transparency.
The above-cited Japanese Laid-Open Patent Publication No. 38787/1975 proposes a process for producing an amorphous random 1-butene/propylene copolymer by performing polymerization at high temperatures using a titanium trichloride-type catalyst. The present inventors, however, have found that these copolymers have a methyl acetate-soluble content of more than 2% by weight, and inferior tensile properties.
Japanese Laid-Open Patent Publication No. 5293/1979 describes a random 1-butene/propylene copolymer containing 1-butene as a main component which has a narrow composition distribution, a low boiling methyl acetate-soluble content and low surface tackiness. The content of low-molecular-weight components in this 1-butene/propylene copolymer, particularly the content of a low-molecular-weight polymer represented by the boiling methyl acetate-soluble content, and the surface tackiness of a molded article prepared from this copolymer are considerably improved over those of 1-butene copolymer obtained by a catalyst system comprising titanium trichloride or titanium tetrachloride. The present inventors, however, have found that the content of the low-molecular-weight polymer in the 1-butene random copolymer, especially the content of the low-molecular-weight polymer represented by the acetone/n-decane mixed solvent (1:1 by volume)-soluble content, is still high, and that a molded article, such as a film, of a resin composition obtained by incorporating the above random 1-butene/propylene copolymer in a polypropylene resin for improved impact strength, tends to increase in surface tackiness with time, and is still unsatisfactory in applications which require high levels of transparency and surface non-tackiness.